A function generator which functions well even at high frequencies is disclosed in the book "Semi-Conductor Circuit Technics" by U. Tietze, Ch. Schenk, 5th Ed., Springer Publishing House (Berlin, Heidelberg, N.Y., 1980) at page 443. This function generator is used for generating a triangle voltage and a rectangle voltage.
The same book discloses on pages 218 and 219 the simultaneous generation of a sine-and-cosine function in the argument range-.pi..ltoreq.x.ltoreq..pi., i.e. over a full period, by means of function networks. To produce such signals, two auxiliary triangle voltages are generated by means of resistor networks and comparators from an input voltage ranging between a positive and a negative limit value. The auxiliary triangle voltages are supplied to sine-function networks.
The same book on pages 488 to 490 teaches the generation of sine-and-cos functions in digital form. The sine-and-cos levels are contained in read-only memories within the scope of a schedule. If high resolution is desired, a great amount of data must be stored to specify the level of the sine and cosine waveforms for different input values. By interpolation between stored values, the storage requirement can be reduced. However, the additional computing time needed to interpolate increases the total time needed to make the function values available.
Finally it is known from the above mentioned book, at pages 646 to 649, to use digital-analog converters for the generation of sine oscillations. A digital input signal corresponding to an increasing and decreasing numerical sequence is applied to an analog multiplexer, the weighting of which is accordingly adjusted.